docs: def quota(cls, id):
          """return disk quota used/free"""
          sampler = {'unit': 'minutes', 'value': 1, 'function': 'avg'}
          query = 'vfs.df.bytes.all'
          metrics = Metric.query(id, 60, query, 'paas', sampler)
  
          df = {'free': 0, 'used': 0}
          for metric in metrics:
              what = metric['size'].pop()
              # we need the most recent points
              metric['points'].reverse()
              for point in metric['points']:
                  if 'value' in point:
                      df[what] = point['value']
                      break
          return df